STM32F427AI datasheet(120/240 Pages) STMICROELECTRONICS

120 / 240 page

Electrical characteristics

STM32F427xx STM32F429xx

120/240

DS9405 Rev 12

Figure 28. Low-speed external clock source AC timing diagram

High-speed external clock generated from a crystal/ceramic resonator

The high-speed external (HSE) clock can be supplied with a 4 to 26 MHz crystal/ceramic

resonator oscillator. All the information in this paragraph is based on the characterization

results obtained with typical external components specified in Table 39. In the application,

the resonator and the load capacitors have to be placed as close as possible to the

oscillator pins to minimize output distortion and startup stabilization time. Refer to the crystal

resonator manufacturer for more details on the resonator characteristics (frequency,

package, accuracy).

Table 39. HSE 4-26 MHz oscillator characteristics (1)

1. Specified by design.

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fOSC_IN

Oscillator frequency

MHz

Feedback resistor

200

kΩ

IDD

HSE current consumption

VDD=3.3 V,

ESR= 30 Ω,

CL=5 pF@25 MHz

450

µA

VDD=3.3 V,

ESR= 30 Ω,

CL=10 pF@25 MHz

530

ACCHSE(2)

2. This parameter depends on the crystal used in the application. The minimum and maximum values must

be respected to comply with USB standard specifications.

HSE accuracy

− 500

500

ppm

Gm_crit_max Maximum critical crystal gm

Startup

mA/V

tSU(HSE(3)

3. tSU(HSE) is the startup time measured from the moment that it is enabled (by software) until a stabilized 8

MHz oscillation is reached. This value is based on characterization and not tested in production. It is

measured for a standard crystal resonator and it can vary significantly with the crystal manufacturer.

Startup time

VDD is stabilized

ai17529

OSC32_IN

External

STM32F

clock source

VLSEH

tf(LSE)

tW(LSE)

90%

10 %

TLSE

tr(LSE)

tW(LSE)

fLSE_ext

VLSEL

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